1 .. SPDX-License-Identifier: GPL-2.0
3 =======================================
4 Internal ABI between the kernel and HYP
5 =======================================
7 This file documents the interaction between the Linux kernel and the
8 hypervisor layer when running Linux as a hypervisor (for example
9 KVM). It doesn't cover the interaction of the kernel with the
10 hypervisor when running as a guest (under Xen, KVM or any other
11 hypervisor), or any hypervisor-specific interaction when the kernel is
14 On arm and arm64 (without VHE), the kernel doesn't run in hypervisor
15 mode, but still needs to interact with it, allowing a built-in
16 hypervisor to be either installed or torn down.
18 In order to achieve this, the kernel must be booted at HYP (arm) or
19 EL2 (arm64), allowing it to install a set of stubs before dropping to
20 SVC/EL1. These stubs are accessible by using a 'hvc #0' instruction,
21 and only act on individual CPUs.
23 Unless specified otherwise, any built-in hypervisor must implement
24 these functions (see arch/arm{,64}/include/asm/virt.h):
28 r0/x0 = HVC_SET_VECTORS
31 Set HVBAR/VBAR_EL2 to 'vectors' to enable a hypervisor. 'vectors'
32 must be a physical address, and respect the alignment requirements
33 of the architecture. Only implemented by the initial stubs, not by
38 r0/x0 = HVC_RESET_VECTORS
40 Turn HYP/EL2 MMU off, and reset HVBAR/VBAR_EL2 to the initials
41 stubs' exception vector value. This effectively disables an existing
46 r0/x0 = HVC_SOFT_RESTART
47 r1/x1 = restart address
48 x2 = x0's value when entering the next payload (arm64)
49 x3 = x1's value when entering the next payload (arm64)
50 x4 = x2's value when entering the next payload (arm64)
52 Mask all exceptions, disable the MMU, move the arguments into place
53 (arm64 only), and jump to the restart address while at HYP/EL2. This
54 hypercall is not expected to return to its caller.
56 Any other value of r0/x0 triggers a hypervisor-specific handling,
57 which is not documented here.
59 The return value of a stub hypercall is held by r0/x0, and is 0 on
60 success, and HVC_STUB_ERR on error. A stub hypercall is allowed to
61 clobber any of the caller-saved registers (x0-x18 on arm64, r0-r3 and
62 ip on arm). It is thus recommended to use a function call to perform